The present invention relates in general to a shock and vibration sensor, and, more particularly, to a shock and vibration sensor for use in a laser transmitter.
Laser systems have been employed in numerous surveying and construction applications. In one such system, a laser light transmitting device provides a rotating laser beam which establishes a reference plane. Typically, the rotating laser beam is used to define, in effect, a continuous plane of light as a constant horizontal bench mark of elevation over an entire work area. The laser light is either detected by the naked eye or by one or more laser beam detectors, placed at considerable distances from the transmitting device. Various construction tasks can be performed based on the visual perception of the laser light. The detectors are used to intercept the rotating laser beam and determine an elevation at selected points throughout the work area. Such detectors may provide a display of the beam height for an operator or, alternatively, may form part of a machine control system that controls or assists in the control of various pieces of equipment, such as for example bulldozers and motorgraders.
In the laser light transmitting device, the generally horizontal plane of light is produced by projecting the beam upward and then deflecting the beam ninety degrees within a pentaprism or penta-mirror assembly. The pentaprism assembly is rotated about a generally vertical axis within the transmitting device to cause the horizontal beam to sweep around the axis and define the horizontal plane. Such a laser light transmitting device includes various components susceptible to damage or misalignment from excessive impact forces or vibrations. It is therefore desirable to provide an indication to the user when the laser light transmitting device has sustained an excessive shock or vibration so that the device may be inspected for any damage to the transmitting device or misalignment of key components. Further, the laser light transmitting device must be capable of sensing excessive shocks or vibrations passively, e.g., when the device is being shipped and at other times when the device is not receiving electrical power.
One type of sensor which can passively monitor shocks and vibrations is disclosed in U.S. Pat. No. 3,909,568 issued to Greenhug on Sep. 30, 1975. Greenhug discloses a sensor in which a pair of opposing balls are supported in a recessed portion of a pair of corresponding arms and separated from each other by a spring. The balls are dislodged upon the application of a predetermined force along the measuring axis of the sensor. The level of this predetermined force is dependent on a number of interrelated factors, such as the unstressed height of the spring, the weight of the balls, the size of the balls in relation to size of the recessed portions of the arms, and the extent to which the spring is compressed when it is in its operative position and the spacing between the balls. Such a sensor is physically large and difficult to reset once tripped. Further, the manufacture of such a sensor is expensive and complicated.
Accordingly, there is a need in the art for a shock and vibration sensor which is simple and inexpensive to manufacture. There is a further need for a shock and vibration sensor which is relatively small in size and simple to reset once triggered.